A brake system of this type is, for example, known from WO 91/18776. The auxiliary reservoir of this known brake system merely serves for providing an additional volume for the slip control. Consequently, the on-off valve in the pump supply line should only open during the slip control. However, such an auxiliary reservoir is also practical if the brake pressure should be additionally built up by means of the pump when the brake pedal is actuated, e.g., for controlling driving stability.
The present invention is based on the objective of additionally improving a brake system of the initially mentioned type with respect to the charging of the auxiliary reservoir.
The present invention achieves this objective by filing the auxiliary reservoir by a separating piston that is displaced from the main brake cylinder toward the auxiliary reservoir. By using this approach, the return pump of an antilock brake system (without slip control) can be designed in nonregenerative fashion.
Due to the medium separation between the brake line and the auxiliary reservoir, the chamber of the separating piston which is connected to the auxiliary reservoir can be directly connected to the pressure medium reservoir without creating an open system. In this case, a return valve arrangement prevents the pressure medium from flowing from the auxiliary reservoir into the main reservoir.
Due to the fact that the separating piston is prestressed toward its first chamber, which is charged by the main cylinder pressure by means of a spring, the chamber on the side of the auxiliary reservoir is automatically refilled when the main cylinder is depressurized.
A stepped design of the separating piston provides an advantageous option for increasing or decreasing the volume between the main cylinder and the auxiliary reservoir. This means that only a small volume on the side of the main cylinder suffices for supplying a significantly larger volume to the auxiliary reservoir.